Method of applying protective wrappings to pipe



June 22, 1965 E, MONULTY ETAL 3,190,780

METHOD OF APPLYING PROTECTIVE WRAPPINGS TO PIPE United States Patent 3,190,780 METHOD OF APPLYING PROTEQTKVE WRAPPENGS TO PIPE Frank E. McNuity and Robert M. Nee, Tulsa, Okla, assignors to Nee & McNulty, Inc, a corporation of Oklahoma Filed May 19, 1961., Ser. No. 114,277 7 'Ciaims. (Cl. 156-162) This is a continuation-in-part of our copending application US. Serial No. 766,065, filed October 8, 1958, now abandoned.

The present invention relates to a novel method of Wrapping a conduit. More particularly it is concerned with an improved method of wrapping long lengths of coated pipelines prior to burial thereof.

Today it is common practice to transport both gaseous and liquid materials distances of many hundreds of miles through pipelines ranging from about 6 to 36 inches in diameter. Natural gas, water, crude and refined petroleum are examples of some of the more important materials transported in this manner.

In protecting these lines from various corrosive agents by first coating the pipe with a primer, which is a solvent solution of an asphalt or tar-like substance, there is placed over the primer a layer of bituminous enamel, usually from about three thirty-seconds to about five thirty-seconds of an inch. Such enamels are Well known to the art and hereinafter it is to be understood that the expressions bituminous enamel or enamel as used in the present description and claims are intended to include any such coating material known to be suitable for the purposes contemplated herein. Owing to the fact that this enamel is subject to cold flow and can be damaged in the process of laying the pipe, or can be readily deformed by soil stress, etc. after the line has been laid, the enamel must be strengthened and reinforced by means of a protective layer. This reinforcing material usually consists of a flexible sheet of glass fiber mat. Properly applied, this reinforcing material should penetrate the fresh enamel to a depth generally corresponding to about one-third of the thickness (measured inwardly from the outside surface) of the enamel coating. The reinforcing sheet itself is preferably impregnated with the enamel.

One of the most serious problems encountered in maintaining a satisfactory coating on pipelines during their use, results from the fact that in transporting fluids, such as gas, through the lines by means'of compressor stations spaced, forexample, to 40 miles apart, the gas issuing from the discharge side of the compressors is quite hot i.e. l-200 F. Moreover, it has been observed that for distances as much as 20 miles downstream from the compressor station, the gas still may have a temperature as high as 170 F. Such high temperatures obviously tend to soften the enamel, causing it to fiow from the top of the pipe, around the side and down to the underside thereof, leaving only a thin enamel film on the major surface area of the pipe to protect it from corrosive agents. In some cases the enamel coating has completely flowed away, leaving bare pipe exposed to a corrosive environment.

The glass fiber mats used in wrapping pipelines are usually about 20 mils thick and are made of small glass fibers dispersed in and held together by asuitable resin. 7

Because of the random distribution of the fibers in the resin and because of the relatively small percentage of glass fibers therein, these sheets are not very strong. Another disadvantage of these mats is that due to their thickness it is not practical to use long lengths of this material on wrapping rolls of line traveling wrapping machines because such rolls are too bulky and heavy for satisfactory operation. As a result, particularly with the larger diameter pipe, wrapping operations are being constantly interrupted to reload a new roll or spool of glass matting on the wrapping machine.

It has been known for some time that woven glass fabric or textile grade glass cloth, because of its durabilityand strength, is an excellent protective coating for line pipe. However, when this material was used for wrapping pipe, having a relatively thick coating of enamel thereon, it was found that the fabric penetrates through the enamel to the primer coat which is next to the pipe. This is due to the tension exerted by the wrapping machine arm on the glass cloth being applied to the pipe. Therefore, the glass cloth lying next to the pipe with practically all the enamel on top of the cloth, is unable to lend any structural or mechanical support to the enamel itself.

Accordingly it is an object of our invention to provide a method by which woven glass cloth or fabric or equivalent material may be applied as a reinforcing and protective material for bituminous enamels used to coat pipelines and similar conduits. It is another object of our invention to provide a novel method for wrapping an enamel coated pipeline with a highly porous or open mesh wrapping material by placing the latter onto said enamel under substantially no tension, whereby said wrapping material is imbedded into the enamel only a relatively short distance.

It is still another object of our invention to provide a satisfactory, relatively thin Wrapping material capable of being placed in extremely long lengths on conventional spools of line traveling wrapping machines.

In one embodiment of our invention, we interroll substantially equal lengths of glass cloth of suitable porosity and another conventional material such as kraft paper or asbestos pipeline felt. The glass cloth is arranged on the roll so that in the wrapping operation it is next to the enamel side of the pipe while the kraft paper rides on top of the glass cloth. Also, in forming this roll of the two materials, the glass cloth should be wound thereon so that the free end of the cloth overlaps the corresponding end of the kraft paper. When applied to the pipe however, the ends of the two wrapping materials are preferably placed in line with one another, thus leaving a small amount, for example, from about one-half to two inches, of slack in the glass cloth. Alternatively, the two layers of wrapping material may be put on the roll or spool in equal lengths. Then when the wrapping operation is begun, the free end of the paper layer may be afiixedto the enamel first with the underneath layer of glass cloth being placed on the enamel an inch or two behind the end of the paper. In this manner suflicient slack in the 7 glass fabric layer is created to permit said fabric to be laid on the enamel in accordance with our invention.

Substantially all the tensionv exerted by the wrapping machine arm during the wrapping operation is on the kraft paper. As a result, glass cloth is laid onto the enamel in the substantial absence of any tension with the paper serving as a vehicle or a guide for the cloth;

Under wrapping conditions of this sort the porous glass cloth sinks into the enamel to a depth corresponding to approximately one-third of the thickness (measured inward from the outside surface) of the enamel coating. With the cloth in this position, it has enamel on both its top and bottom sides, thereby tending to impart maximum reinforcing and mechanical strength to the coating. Our invention may be further illustrated by reference to the accompanying drawings in which FIGURE 1 is an isometric view showing a pipeline wrapping operation using the method of our invention. FIGURE 2 is a sectional view taken at 2 in FIGURE 1 showing in detail the structure of the wrapping on the pipe. FIGURE 3 is a modification of FIGURE 2 in which a thermoplastic film is substituted for the inner layer of glass cloth.

Referring again to FIGURE 1, a line pipe 1 is covered with a relatively thick coating of enamel 4. The line pipe is held by a conventional line traveling machine 6 shown only in a fragmentary view. Wrapping arms 8 are operated by wrapping head 10. The wrapping arms hold rolls 12 containing strips of interrolled glass cloth 14 and kraft paper 16. The tension exerted on the kraft paper may be controlled by turning knobs 18 which regulate the breaking action exerted on spools 20. While the ends of the paper and the cloth are even as the two strips are wrapped onto the coated pipe, the glass cloth strip is slightly longer causing a small loop 22 therein next to enamel 4. This allows the cloth 14 to be laid substantially without tension onto the enamel. The glass cloth sinks slightly into the enamel and becomes impregnated therewith as shown in some detail in FIG- URE 2.

The latter figure is an enlarged sectional view of a wrapped portion of the pipe shown in FIGURE 1 illus trating how glass fabric 14 partially sinks into enamel layer 4. Under the conditions provided by the method of our invention a relatively thin layer 17 of enamel lies between the fabric 14 and paper layer 16 thus forming a firm compactly wrapped pipe capable of giving many years of uninterrupted service.

In fragmentary FIGURE 3, the glass cloth or other coarsely woven fabric 14 has been replaced by thermoplastic layer or film 24. It will be seen that in this embodiment the plastic film rests on the surface of enamel 4 since the latter does not penetrate said film. In using a plastic film next to enamel 4, in accordance with our invention, it will be appreciated, of course, that while outer layer 16 may be of kraft paper, it need not necessarily be since the enamel does not pass through film 24. Thus, outer layer 16, the essential purpose of which is to serve as a carrier for slack film 24, may be perforate or imperforate since the plastic film, itself, prevents any enamel from flowing through to the outer layer or layers.

The glass cloth or fabric used in carrying out our invention should be of a sufiiciently coarse weave to permit relatively rapid impregnation of the enamel. Generally speaking, glass cloth having no more than about 34 by 38 threads to the inch should be used. Ordinarily, cloth woven to have from by to 26 by 34 threads to the inch is preferred. The expressions glass cloth or woven glass fabric or woven glass textile cloth as used herein are intended to be limited to wrapping material with the aforesaid characteristics.

For glass cloth, as employed in our invention, a suitable thermoplastic film may be substituted. The use of such plastic film offers numerous advantages; however, prior to the present invention no method, to our knowledge, has been known by which the plastic film could be applied to a hot enameled surface. The principal difiiculty in this regard has been due mainly to the fact that the application temperature of the coal tar or similar enamel may be as high as 500 F. At temperatures of this magnitude thermoplastic film has very little if any tensile strength. Accordingly, at such temperatures it is impossible to cover the enameled surface with film of the aforesaid kind by conventional wrapping methods.

By the process of our invention, however, thermoplastic films such as, for example, polypropylene, high or low density polyethylene, etc., from about 1 to about 7 mils in thickness, may be applied to a pipeline coated with hot enamel. No slack need be present in said film during the wrapping step. It is satisfactory for said film to lie fiat on or be supported by the outer wrapper layer of kraft paper or the like. No tensions should be exerted on said film while wrapping in contact with the hot enamel, however. While said film has substantially no tensile strength at temperatures of from about 300 to about 500 F., it is adequately supported by an outer layer or strip of kraft paper, glass cloth or similar wrapping material with which it is interwound on the wrapper spool. In this way, said outer layer serves to carry the thin plastic film plus the hot applied enamel which has a tendency to run or flow at temperatures employed during the wrapping operation. Under these conditions a wrapping of thermoplastic film is placed about the conduit without any stress being exerted on said film while the wrapping operation takes place. However, when the line wrapped in this manner is allowed to cool the plastic film regains its original tensile strength thus providing a high quality shield for the bituminous coating.

Films of the aforesaid type can be employed in accordance with our invention even where relatively high temperatures, for example, F., are encountered in the line such as is true in the case of the discharge side of a compressor station. High density polyethylene, which retains good tensile strength and hardness up to temperatures of about F., is well suited to applications of this type.

It will be apparent to those familiar with this art that numerous modifications may be made in our invention without departing from the scope thereof. While our invention is directed primarily to a means of wrapping enamel-coated conduits in general, it may be said that in its broader embodiments, the invention contemplates a method for wrapping a conduit with a roll having a first layer of sheet-like material interrolled with a second strip or sheet of the same or different material, creating slack in the strip next to said conduit, winding said roll about said conduit so as to keep tension substantially only on said second strip whereby said first sheet is guided onto said conduit without substantial tension.

We claim:

1. A method of wrapping a pipe covered with a hot flowable coating of enamel which comprises, affixing the free ends of a plurality of layers of protective sheet-like material to the enameled surface of said pipe, at least the outer layer of said material being impervious to said enamel, maintaining substantially no tension on the inner layer of said material next to said enamel while exerting substantially all the tension required to effect the wrapping operation on the other of said layers, and thereafter spirally wrapping said pipe with said material while said enamel is in a hot fiowable condition, said layers being superposed on one another and unwound from the same source onto said pipe.

2. The method of claim 1 in which the layer of wrapping material next to said enamel is glass cloth.

3. The method of claim 1 in which the layer of wrapping material next to said enamel is a thermoplastic film.

4. The method of claim 3 in which the thermoplastic film is polyethylene.

5. The method of claim 3 in which the thermoplastic film is polypropylene.

6. The process of claim 1 in which the layer of material next to said pipe is a woven fabric having not more than about 34 by 38 threads to the inch.

7. The method of claim 3 in which the enamel is at a temperature ranging from about 300 to about 500 F.

References Cited by the Examiner UNITED STATES PATENTS 3,024,153 3/62 Kennedy 156-187 3,033,724 5/62 Stokes 156-187 EARL M. BERGERT, Primary Examiner. 

1. A METHOD OF WRAPPING A PIPE COVERED WITH A HOT FLOWABLE COATING OF ENAMEL WHICH COMPRISES, AFFIXING THE FREE ENDS OF A PLURALITY OF LAYERS OF PROTECTIVE SHEET-LIKE MATERIAL TO THE ENAMELED SURFACE OF SAID PIPE, AT LEAST THE OUTER LAYER OF SAID MATERIAL BEING IMPERVIOUS TO SAID ENAMEL, MAINTAINING SUBSTANTIALLY NO TENSION ON THE INNER LAYER OF SAID MATERIAL NEXT TO SAID ENAMEL WHILE EXERTING SUBSTANTIALLY ALL THE TENSION REQUIRED TO EFFECT THE WRAPPING OPERATION ON THE OTHER OF SAID LAYERS, AND THEREAFTER SPIRALLY WRAPPING SAID PIPE WITH SAID MATERIAL WHILE SAID ENAMEL IS IN A HOT FLOWABLE CONDITIN, SAID LAYERS BEING SUPERPOSED ON ONE ANOTHER AND UNWOUND FROM THE SAME SOURCE ONTO SAID PIPE. 